Elastic polyurethane fibers are widely used in sport clothing such as swimming costumes and stockings, general clothing such as innerwear, outerwear, and stockings, hygienic articles such as diapers, and industrial materials.
When elastic polyurethane fibers are used in these articles, elastic polyurethane fibers which can provide the articles having a lower thickness, a lighter weight, and a higher performance are increasingly demanded. Especially in recent years, interest has been focused on products such as sport clothing and innerwear with enhanced fit during wear, and stockings and girdles which provide higher support during wear compared with related articles and which have a superior ability to temporarily alter the wearer's body shape and a superior ability to reduce fatigue. These sectors have strongly demanded an elastic polyurethane fiber which imparts comparable stretch in a smaller amount relative to related fibers to provide a thinner fabric having a lighter weight and a high transparency, and which imparts higher stretch in the same amount to provide a higher function.
As used herein, “stretch” refers to stretch stress related to resistance when clothes are about to be worn and recovery stress related to fit when clothes are being worn. Higher stretch stress is not always preferred. When clothing has an extremely high stretch stress, the clothing is made difficult to stretch and hard to put on. Thus, clothing which has a similar stretch stress compared to the related articles and thus is easy to put on and which has a higher recovery stress and a higher fit compared with the related articles is demanded. In other words, an elastic polyurethane fiber, having a high recovery stress and a low hysteresis loss after stretch and recovery is demanded. An elastic polyurethane fiber having a high heat resistance closely related to the processability such as knitting, weaving, and braiding is also demanded.
Patent Document 1 discloses an elastic polyurethane fiber which includes a polyurethaneurea prepared from a copolyalkylene ether diol including different C2-10 alkylene ethers, the polyurethane including urethane moieties and urea moieties having a number average molecular weight within a specified range. Although the elastic polyurethane fiber has a low hysteresis loss, the elastic fiber has a low recovery stress, because the polyurethane is designed to provide a low stretch stress.
Patent Documents 2, 3, 4, and 5 described below disclose an elastic polyurethane yarn prepared by, for example, using a specified copolyether diol or combining various diamines to provide certain characteristics such as soft stretch, easy set, and damp heat creep resistance. With these methods, however, it is difficult to produce an elastic polyurethane fiber having a high recovery stress, a low hysteresis loss, and a high heat resistance.